Many people experience pain in a joint, such as the knee, elbow, neck, finger, and the like. Much chronic joint pain consists of osteoarthritis characterized by damage to cartilage that protects bone surfaces. Once damaged cartilage regrowth is difficult. Treatment for a damaged joint is limited and may include external bracing, lubricative or anti-inflammatory joint injections, analgesics, or ultimately replacement of the joint with a prosthesis.
Supportive muscle strength and high joint activity may improve long prognoses, yet most of the aforementioned treatment options are inconsistent with the physical activities necessary to retard or prevent disease progression. External bracing, for example, may cause atrophy of the very muscles needed for joint support. Sedation, as another example, discourages high activity. Thus, devices that actively stimulate the body's own musculature surrounding the compromised joint may help rehabilitation. Some such devices are worn throughout the day, constantly monitor the patient's movements, and respond to problematic joint forces by stimulating muscles opposing the incident force causing the problem.
A form of muscle stimulation used in these devices is electrical current. Electrical stimulation that creates a direct current (DC) bias across a muscle, such as galvanic stimulation or unidirectional pulsed waveforms, induces hydrolysis under the electrodes and may cause pain at higher currents. Pure alternation current (AC) (sometimes called symmetric biphasic or polyphasic) waveforms that present no DC component across a muscle may therefore be used for higher stimulation currents. This facilitates maximal contractile effect with less patient discomfort.
In other words, therapy for injured joints still fails to properly balance supporting the joint while fostering rehabilitation of the joint.